Television synchronizing system



Aug. `4, 1942. R`E MOE 2,292,148

E TELEVISION SYNCHRONIZING SYSTEM Filed July 23, 1940 2 sheets-sheet 1 LT/Mf J2e Inventor:

Robert/ .M e;

b JV XJ yHiaZt-borhef Aug- 4, 1942. R. E. MOE k 2,292,148

TELEVISION SYNCHRONIZING SYSTEM l Filed July 23, 1940 2 Sheets-Sheet 2 C34. VER T/cAL DEFLEOT/OM HHPL lF/ER Inventor: Robert E M e Patented Aug.4, 1942 TELEVISION SYNCHBONIZING SYSTEM Robert E. Moe, Bridgeport,Conn., assigner to General El New York ectrio Company, a corporation o!application July 2s, 1940, serial No. 346,898

(ci. 17a-69.5)

11 Claims.

My invention relates to a television synchronizing system, andparticularly to a method and apparatus whereby the scanning action of atelevision receiving system may be maintained in accurate synchronismwith the scanning action of a television transmitting system.

In present day television systems utilizing cathode ray dischargedevices for generating a.` picture signal at the transmitter and forreproducing the image at the receiver, means must be provided forsynchronizing their operation. rdinarily, in the transmitting picturesignal generator the horizontal synchronizing signal is generated duringeach retrace interval following the end of each horizontal line tracedby the cathode ray; and during the ily-back interval following the endof each picture eld traversed by the ray, a vertical synchronizingvsignal is generated. These signals are combined with the video signal,which is representative of thelight and shade values o! the image beingscanned, and the complete signal ls modulated upon a transmittedcarrier. At the receiver a second cathode ray is caused to scan ailuorescent screen in a similar pattern. The intensity of this ray iscontrolled in accordance with the detected'video signal in order toreproduce the image. The horizontal and vertical synchronizing signalsare separated from the video signals and utilized to trigger thehorizontal and vertical deflection generators respectively. In this waythe two cathode rays at the transmitter and receiver are maintained insynchronism, as is well understood by those skilled in the art.

According to present television practice, the transmitted synchronizingsignal is composed of substantially'rectangular pulse components. All ofthese are of substantially equal amplitude, but their time durations aredifferent. Generally, the vertical synchronizing pulse componentstransmitted at the end of each picture field are of much greater timeduration than the other pulses. Integrating circuits are employed in thereceiver to derive a distinctive signal from these long pulses which isutilized to eiect synchronization of the vertical ray deflectiongenerator.

It is a main object of my invention to provide an improved method andapparatus for deriving a distinctive synchronizing signal from one ofthe pulse components of the received composite synchronizing wave.

It is a further object of my invention to provide an improved method andapparatus for separating one group of synchronizing pulse componentsfrom a composite synchronizing wave and for shaping them to providesynchronizing impulses which are eminently suited for accuratetriggering of one of the deflection generators.

More specically, in accordance with my invention means are provided forderiving, from those pulse components of longest duration in thereceived synchronizing waves, a' series of synchronizing pulses, each oiwhich\has a sharply dened maximum peak.y Dile to the wave form of thesederived pulses, highly accurate synchronization is obtainable and thepossibility of false triggering and the consequent loss of synchronismis greatly minimized.

The features of my invention which I believe to be novel are set forthwith particularity in the appended claims. My invention itself, however,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawings, in winch Fig. 1 is a diagrammatic view,partly schematic, of a television receiving system embodying myinvention; Fig. 2 is a group of curves illustrating the forms of wavesdeveloped at various points in the receiving system of Fig. 1; Fig. 3 isa diagrammatic view, partly schematic, of a slightly modiiied form oftelevision receiving system embodying my invention, and Fig. 4 is adiagrammaticV view of a modification of that portion of the circuit ofFig. 3 indicated within the coniines of the dashed rectangle.

In the television receiving apparatus of Fig. 1 a transmitted televisionsignal is received by the antenna i0 and a picture image correspondingto this signal is reconstructed by means of the cathode ray dischargedevice Il. Those elements of the receiving apparatus which may beconventional have been indicated in block form to simplify the drawing.Thus, as indicated, the received signal is impressed upon radiofrequency amplifiers and a converter, indicated by the block l2. It isthen supplied through the intermediate frequency amplifiers and Jseconddetector, indicated by the block I3, and throughv the video ampliiiers,indicated by the block i4, to an intensity control element of thecathode ray discharge device il.

The cathode ray device l l may be of any wellknown form and the detailsthereof form no part of my invention. Means are provided therein fordeveloping and projecting an electron ray against a fluorescent screenon the end of the tube envelope. The intensity of the ray is varied inaccordance with the intensity of the signals applied to the controlelement from the video ampliiier il. At the same time the ray is caused`to scan the screen in a pattern similar to that scanned by the cathoderay in the transmitting apparatus. In the embodiment illustrated in Fig.1, this action is eifected by the pairs of magnetic defiecting coils l5and I6 which cause the ray to be deflected along two coordinate axes.

The received television signal also contains, the same channel, thecomposite synchronizing signal. The output of the second detector isalso impressed upon the synchronizing pulse separator, indicateddiagrammatically by the block Il. In the separator l1 the synchronizingwave is separated from the video signal in a manner well known to thoseskilled in the art.

The composite synchronizing wave is impressed upon the control grid of athermionic amplifier i8. One form of synchronizing wave now in commonuse is illustrated graphically by the curve 50 in Fig. 2. The wave formof this signal is well known and will not be discussed in much detail.The form is that recommended by the Television Committee of the RadioManufacturers Association. For further infomation reference is made toan article in "Electronics magazine for July, 1938, pages 28 and 29,entitled R M A completes television standards.

Brley, the composite synchronizing wave is composed of a plurality ofessentially rectangular pulses. These are of substantially the samemaximum amplitude but they are of different widths and recur atdifferent fundamental frequencies, The pulses 5I are thehorizontalsynchronizing pulses transmitted at the end of each pictureline. In systems employing interlaced scanning, equalizing pulses 53 may.be transmitted during the interval between successive picture eldspreceding and following the vertical synchronizing signal 52. Theequalizing pulses 53 are narrower than the horizontal synchronizingpulses 5I and recur at a higher fundamental frequency. Their function isto remove all influence of the unequal time intervals existing betweenthe horizontal and vertical synchronizing pulses in alternate pictureelds when interlaced scanning is employed, as is Well known in the art.This forms no part of my invention. For a further understanding of thefunction of the equalizing pulses reference may be had to Patent No.2,192,121, Alda C. Bedford, issued February 27, 1940.

For reasons that will be apparent to those skilled in the art, the longvertical synchronizing pulses 52 are slotted at the frequency of theequalizing pulses 53, so that synchronization of the horizontaldedection circuits may be maintained dln'ing the vertical synchronizingperiod.

As illustrated in Fig. l, the amplified synchronizing signals 5I!appearing in the anode circuit of the amplifierv I8 are coupled to thehorizontal deection circuits, indicated schematically by the block 20,by means of the transformer I9.

The horizontal deflection circuits 20 include suitable multivibrator orsweep oscillator circuits for generating deflection currents ofpredetermined wave form which are supplied to the coils I6 to deect thecathode ray horizontally in the conventionali manner As is well known,such circuits can be readily synchronized by the injection of a relatedpotential of the proper char'- acteristics. Thus, in the illustratedembodiment, the deflection circuits 20 may be synchronized at theleading edges of the pulse components of curve 50 at the pointsindicated by the arrows. These points recur at the line scanningfrequency at all times and thereby 'maintain synchrnism of thedeflection circuits 20 during the yback interval as well as during thescanning of each field. This method of operation is well known to theart and is mentioned only briefly for the sake of completeness.

In accordance with my invention a distinctive vertical synchronizingsignal is also derived from the wave 5|! appearing in the output-of theamplifier II. This is utilized to synchronize the vwith respect to theamplitude scanning action of the vertical deflection circuits of thecathode ray device Il in a manner now to be described more in detail.

'Ihe output of the amplifier i8 is coupled to the control grid of athermionic device 2| by means of a time constant network, comprising acapacitor 22 and a resistor 23 connected in parallel therewith through asuitable source of operating potential for the amplifier i8. This sourceis not shown but is indicated as having a positive terminal'thereofconnected to the lower end of i resistor 23.

The. time constant of the network 22-23, i. e., the product of thecapacitance of 22 in farads and the resistance of 23 in ohms, is sochosen that a partial integration of the synchronizing wave 50 iseilected in order to produce amplitude discrimination between thevarious pulse components of the wave. The wave form of the synchronizingwave appearing at point 25 in Fig, l is illustrated graphically by thecurve 50a in Fig. 2. It will be observed that the substantiallyrectangular pulses 5I, 52 and 53 of curve 50 have now been deformed Ainto the corresponding peaked pulses 5|a, 52a and 53a of the curve 50aas the result of the partial by the time constant network 22-23.Furthermore, the capacitor 22 is charged to a much higher averagepotential during the occurrence of the long vertical synchronizingpulses 52 than during the relatively short horizontal synchronizingpulses 5I and equalizing pulses 53. "Consequently, the average amplitudeof the wave 50a is greater during the occurrence of the pulses 52a thanduring the occurrence of the pulses 5la and 53a. Due to the slotted waveform of the pulses 52 the capacitor 22 is partially discharged andrecharged a plurality of times during each pulse, producing the serratedwave form characteristic of the pulses 52a. v

The wave form of the' various pulse components of Wave 50a is of coursedetermined by the logarithmic charge and discharge characteristics ofthe network 22-23. The propertime constant of the network is determinedby two principal considerations. It must be high enough to cause apartial integration of the wave suflicientito increase the amplitude ofthe pulses 52a of the other pulse components of the wave. At the sametime, and for reasons that will shortly be apparent, it is highlydesirable to retain as far as possible the steep slopeof the edges 0fthe pulses 52. In other words, the time constant of the network must below enough so that the edges54a of the pulses 52a have a relativelysteep slope.

Expressed another way,-it may be stated very generally that the timeconstant of the network 22-23 should be substantially greater than thetime duration of a horizontal synchronizing or equalizing pulse 5I or 53and less than the time interval occupied by a vertical synchronizingpulse 52, If these relationships are observed, suiilcient amplitudediscrimination between the various componentsgwithout too muchdistortion of the vertical synchronizing signal can be readily effected.

The time constant not sharply critical. obtained as longas integrationproduced' vfactory results were obtained with the time con# stant ofthis network lying between approximate'- ly 50 and200 microseconds.

The wave a appearing at the point 2l is supplied to the grid of thetriode amplifier 2l through the coupling capacitor 26 and grid re'sistor 21. The entire output load of this amplifier, comprising theresistor 2l, is included in the common cathode return circuit. Thetriode 2l is arranged to operate as a clipper in a well known Briefly,the anode potential is maintained quite low and the grid is self biasedby means of the capacitor 2i and resistor 21. The grid bias issumciently great to prevent the ilow of anode current except when theimpressed signal exceeds a predetermined minimum value. In

the embodiments illustrated in Figs. l and 2 anode current flows onlywhen the magnitude of the wave 50a. exceeds a predetermined clippinglevel, indicated by the dashed line l5.

The potential appearing across the output load resistor 2t isillustrated graphically bythe curve- Slb in Fig. 2. It will be observedthat only those portions of the pulses 52a appearing above the clippinglevel 55 are present. The partially integrated horizontal synchronizingand equalizing pulses Sla and 53a are not transmitted since they arebelow this level.

The potentials appearing across the resistor 23 are utilized tosynchronize the operation of the vertical deflection circuits in amanner to be described'shortly. Currents for energizing the deondarywinding of the transformer 32 through the grid capacitor 35 and gridresistor 26 which provide a self bias for the grid. synchronizingpotentials derived from the resistor 28 are impressed on the grid of thedevice lll'through the coupling capacitor 31.

The operation of the blocking oscillator 25 is, for the most part,conventional. However, it will be described briefly. Assume first thatthe oscillator is inoperative, and that anode potential has just beenapplied to the device 30. Since there is zero bias on the grid, anodecurrent immediately begins to flow. The transformer 22 is so connectedthat the flow of anode current through the primary 'winding thereofproduces a voltage on the secondary winding which drives the gridpositive'very rapidly. As the anode current consequently increasesrapidly, the condenser I3 is discharged rapidly. The grid is also biasednegatively through the action of the grid capacitor 35 and the gridresistor 3B. When this -bias reaches the cut-oil value the anode currentabruptly ceases. Capacitor Il now charges from the source of anodepotential through the resistor 34 and the grid bias decreases towardzero. The potentials appearing across capacitor 33, which are generallyof sawtooth wave form. are supplied to the vertical deflection amplifier3| for energizing the vertical deilecting coils I5.

In the absence of any synchronizing impulses to now and the cycle justdescribed will be repeated. InA actual operation the value of theresistor ll is such that a synchronizing pulse B2b appears across theresistor 28 slightly before the grid potential of the device ll reachesthevalue at which anode current begins to flow. Resistor I. ispreferably adjustable so that the unsynchronized frequency of oscillator28 may be varied slightly to obtain yproper triggering.

In accordance with my invention. the wave form of the serrated pulsesB2b appearing across resistor 28 is modiiled so that the synchronizingpulses applied to the grid of amplifier 30 are of a shape particularlysuited for accurate triggering of the blocking oscillator 29.

It will be observed that the capacitor 31 is connected to ground throughthe resistor 3S and also through the grid capacitor lili4 and secondarywinding of the transformer 32. Thesefour circuit elements comprise atime constant network for producing a differentiating action. To thisend the capacitor 3l is made rather small so that it passes the highfrequencycomponents of the pulses52b with greater eiiiciency than thelow frequency components and the impedance of the shunt paths throughresistor 31 and through capacitor 25 and the secondary winding oftransformer 32 are made quite low for 'all components of the pulses.

Each of the serrated pulses 52h can be resolved into a plurality ofcomponent pulses comprising a relatively long pulse of substantiallyrectangular shape. recurring at the field frequency. and a plurality ofhigher frequency components which are introduced by the seri-ations.Through the action of the aforementioned differentiating network, thesynchronizing pulses impressed upon the grid of the amplifying device 30are generally of the form illustrated by the curve c in Fig. 2. It willbe seen that there is a positive, sharply sloped major peak 54C at thecommencement of each synchronizing pulse 52C and a similar majornegative peak Bld at the termination thereof. These major peaks `resultfrom differentiation of the steeply sloped leading and trailing edges ofthe fundamental frequency component of each puise B2b. The higherfrequency lcomponents contained in the serrations are the grid potentialof device lli will next decrease to a value at which anode current againbegins transmitted by the capacitor 3l without substantial change andare effectively superimposed upon the waveform produced by thedierentiation of the fundamental frequency component.

The initial positive peak 54e of each synchronizing pulse 52h is of suchpolarity that it tends to drive the grid of the device 30 more positive.As previously mentioned, this peak occurs just prior to the time thegrid 'potential reaches thek cut-off value as it decreases toward zero.By proper adjustment of the circuits the grid can be made to reach theoperating bias when the potential of the synchronizing pulse reaches avalue. suchas indicated by the point 56, which at least equals orexceeds the maximum values of the other serrations of the pulse 52e.Thus,

the blocking oscillator 29 triggers at the point.

5B of the synchronizing wave 50c and the cycle of operation previouslydescribed is again initiated.

It will now be appreciated that, since the blocking oscillator 29triggers on the sharply sloped portion of the major peak tlc, theinstant of triggering is fixed with great precision.

Further, since it triggers at a potential in excess of the peak valuesof other. portions of the pulse 52e. the possibility of false triggeringon Fig. l only in minor particulars.

one of thesubsequent serrations of the pulse' 52e is practicallyeliminated. V

Merely by way of illustration and not in any sense by way of limitation,the following list of circuit constants is given for a practicaltelevision receiving apparatus constructed in accordance with Fig. 1 anddesigned for operation on a 441 line, double interlaced televisionsystem, having a field frequency of 60 cycles per second:

Fig. 3 is a diagrammatic view of a television receiving apparatus whichdiffers from that of Corresponding reference labels and numerals havebeen placed upon the two figures to facilitate their comparison.

The circuit of Fig. 3 differs essentially from that of Fig. 1 only inthe arrangement of the circuits of the amplifier |`8 and the clipper 2l. The amplifier I8 has its output load resistance 60 in the commoncathode return. The synchronizing wave is applied to the horizontaldeflection circuit 20 over the conductor 6I from the cathode end of thisresistor. Thus the transformer i9 can be eliminated, resulting insimplification of the circuit and increased economy. y

The capacitor 64. of the integrating circuit is connected between theanode and cathode of the amplifier I8 through the grid couplingcapacitor 62 for the clipper 2|. The anode supply resistor 63 completesthe time constant network, by means of which the partial integration,previously described in connection with Figs. 1 and 2. is accomplished.

'I'he grid resistor 65 for the clipper 2l is connected between the gridand ground in this modi- 'iication The anode of the.clipper 2l isconnected toa source of low positive potential, as

before, and the 4output load of resistance 66 is included in the commoncathode return lead.

The operation of the circuit illustrated in Fig.

3 is substantially the same as thatalready described in connection withthe circuit of Fig. 1

and it is thought unnecessary to repeat it here. The following circuitconstants are given as being illustrated in Fig. 4. Except for thesubstitution of the diode l0 for the triode 2|, the circuit elements andconstants are substantially the same. The only material reason forpreferring a triode to a diode for the clipper is the higheramplification obtainable, as`will be apparent to those skilled in theart.

It will'thus be apparent from the foregoing that I have provided animproved method and apparatus for separating one group of synchronizingpulse components from the composite synchronizing wave and for shapingthem to provide sharply defined synchronizing potentials. While notlimited thereto, it will also be apparent that they are particularlyeffective for accurate 'triggering o f the vertical deflectiongenerator. It should also be noted here that the sequence of operation,i. e. the partial integration, clipping and final differentiation, areimportant. The differentiation would be of no value if performed priorto the clipping operation since it would tend to accentuate the higherfrequency components,

' including the horizontal synchronizing and equalmerely illustrative ofthose which have been found to be satisfactory in actual practice in theY circuits of Fig. 3 when employed in a 441 line,

double interlaced system, having a fleld frequency of cycles per second.

Capacitor 62:.05 mfd. Resistor 63=10,000 ohms Capacitor 64:.02 mid.Resistor-'65:22 megohms Resistor 66=10,000 ohms The other circuitconstants previously given for Fig. 1 remain the same.

The triode clipper 2| illustrated in Figs. ll and 3 may optionally bereplaced by a diode type of clipper with satisfactory results. Forexample, that portion of Fig. 3 within the confines of the dashedrectangle may be replaced by the circuit izing pulses, and to reducevthe vertical synchronizing component. Therefore, the effect of theprevious partial integration would merely be nullified. However, oncethe horizontal synchronizing and equalizing pulse components have beenremoved by the clipping operation, the dinerentiating operation maybe'performed with the materially improved results obtainable inaccordance with my invention.

In the embodiments of my invention illustrated and described herein, ithas been stated that synchronization of the deflection circuits iselected on the leading edges of the synchronizing signals. This is notto be construed as limiting, since it will be apparent to those skilledin the art that effective results are obtainable by synchronizing on thetrailing edges of the egnals. Thus, for example, it will be observedthat the peak 54d of the wave 50c in Fig. 2 might also be used forsynchronizing if minor changes were made in the circuits to permit theapplication of the synchronizing pulses in the proper polarity. However,it is the more customary practice to synchronize on the leading edges ofthe pulses and, in general, this will be preferable since it allows moretime to complete the retrace.

While I have shown particular embodiments of my invention, it will ofcourse be understood that I do ,not Wish to be limited thereto sincevarious modifications may be made, and I contemplate by the appendedclaims to cover any such modiilcations as fall within the true spiritand scope of my invention.

What I claim as nevi and desire to secure by Letters Patent of theUnited States is:

1. In the art of television, the method of deriving synchronizingimpulses from a composite synchronizing wave composed of a plurality ofcomponent pulses of comparable amplitudesand of substantially differenttime durations, certain pulse components of relatively long durationhaving steeply sloped leading edges, comprising the steps of effecting apartial integration of said wave just sufficient to increase therelative amplitude of said pulse components of greater duration ascompared with the amplitudes of other components of said wave while yetretaining a an'aaus tively lower frequency, all said component pulsesbeing of substantially equal amplitude and having steeply sloped leadingedges, comprising the steps of integrating said composite wavesumciently to increase the amplitude of said wave during the occurrenceof said long pulses as compared with the amplitudes of other portions ofsaid wave without materially decreasing the slopes of said edges,transmitting said portions of greater amplitude and differentiating saidlastmentioned portions to provide synchronizing impues each of which hasa sharply sloped major De 3. In the art of television, the method ofderiving synchronizing impulses from a composite synchronizing wavecomposed of a plurality of component pulses of comparable amplitudes andof substantially different time durations. all of said pulses havingsteeply sloped sides, comprising the steps of integrating said compositewave suillciently to increase the amplitude of those pulse components ofgreater duration with respect to the amplitudes of other components ofsaid wave without materially decreasing the slopes of said sides,transmitting only said lastnamed components of greater amplitude anddifferentiating said transmitted components to provide synchronizingimpulses each of which has a sharply sloped major peak.

4. In the art of television, the method of deriving synchronizingimpulses recurring at the ileld scanning frequency from a compositesynchronzing wave composed of short pulse components recurring atfrequencies at least as high as the line scanning frequency vandrelatively long pulse components recurring at the field scanningfrequency, all said component pulses being of substantially constantamplitude and at least said long pulse components having steeply slopedleading edges, comprising the steps of effecting a partial integrationof said wave just suicient to increase the relative amplitude ofportions of said wave during the occurrence of said long pulses ascompared with the amplitudes of other portions of said wave while yetretaining a relatively steep slope to said leading edges, clipping offsaid portions of greater amplitude and differentiating said lastmentioned portions to provide synchronizing impulses each of which has asharply defined major peak.

ration of greater amplitude than subsequent serrations.

6; synchronizing pulse separation apparatus for deriving synchronizingimpulses from a composite synchronizing wave composed of a plurality ofcomponent pulses of `comparable amplitude and substantially diierenttime durations, certain pulse components of relatively long durationhaving steeply sloped leading edges, comprising, in combination, meansfor effecting a partial integration of said wave just suicient toincrease the amplitude of said pulse components of greater duration withrespect to the amplitudes of other components of said wave while yetretaining a relatively steep slope to said leading edges, means fortransmitting only said last named components of greater amplitude, andmeans for differentiating said. transmitted components to providesynchronizing impulses each of which has amaJor peak.

7. In synchronizing pulse separation apparatus adapted to developsynchronizing pulses from a composite synchronizing wave composed ofsubstantially rectangular pulse components of comparable amplitudes andsubstantially different widths, the combination of means comprising anintegrating transmission network for distorting said wave to producesubstantial variations in the amplitudes of said components directly inac- 5. In the art of television, the method of deriving iieldsynchronizing impulses from a composite synchronizing `wave composed ofpulse components all of substantially equal amplitude and rectangularwave form, said components including relatively short pulses recurringat a high frequency equal to the line scanning frequency or a multiplethereof and relatively long pulses recurring at the eld scanningfrequency, each of said long pulses being interrupted for shortintervals at one of said high frequencies, comprising the steps ofpartially integrating said composite wave suiliciently v to distort saidshort pulses into peaked pulses and said long pulses into serratedpulses of relatively 7o greater amplitude, clipping off portions of saidserrated pulses at a level exceeding the amplitudes of said peakedpulses, and diiferentiating said portions sumciently to provide serratedfield synchronizing impulses each having an initial sercordance withtheir widths, said network having a time constant substantially lessthan the durations of those pulse components of greatest width andgreater than the durations of the remaining components of said wave, athermionic discharge vdevice having input and output circuits, means forcoupling said wave to said input circuit through said integratingnetwork, means biasing said device so that it passes current in itsoutput circuit only during portions of said integrated wave exceeding apredetermined amplitude clipping level, and means comprising adifferentiating network in said output circuit for peaking the outputcurrent wave to provide sharply defined synchronizing pulses.

`8. synchronizing pulse separation apparatus for deriving synchronizingimpulses from a composite synchronizing wave composed of short pulsecomponents recurring at high frequencies and relatively long pulsecomponents occurring at a relatively lower frequency, all said componentpulses being of comparable amplitudes and having steeply sloped leadingedges, means for effecting a partial integration of said wave sul-.cient to increase the amplitude of said long pulse components withrespect to the amplitude of said short pulse components, said meanscomprising an integrating network having a time constant substantiallygreater than the duration of said short pulse components and less thanthe duration of said long pulse components, means for transmitting saidpartially integrated wave only during the occurrence of those portionsof increased amplitude, and means for modifying thewave shape of saidtransmitted portions to provide synchronizing impulses each of which hasa sharply sloped major peak, said last means comprising adifferentiating network.

9. In a television receiving system, in combination, means for receivinga composite synchronizing wave composed of short pulse componentsrecurring at high frequencies and relatively long pulse componentsrecurring at a relatively lower frequency, all said component ,pulsesbeing of substantially constant amplitude4 and having steeply slopededges, a thermionic discharge device having input andoutput circuits,means for coupling said receiving means to said .input circuit and formodifying its wave shape comprising an integrating network, said networkhaving a time constant suiiicient to increase the amplitude of said waveduring the occurrence of said long pulses as compared with the amplitudeof other portions of said wave without materially decreasing the slopeof said edges, means biasing said device to prevent transmission of saidmodified wave to the output circuit thereof except during plitude, andmeans coupling the output ofl said device to the input of said generatorfor synchronizing its operation, said last means comprising a secondnetwork for diierentiating said portions the occurrence of said portionsof increased amplitude, a utilization circuit, and means coupling saidoutput circuit to said utilization circuit, said last means comprising adifferentiating network for further modifying the wave shape of saidtransmitted portions to provide synchronizing impulses each of which hasa sharply sloped major peak.

l0. In a television system wherein a i'leld deyection generator issynchronized from impulses derived from a composite synchronizing wave,said Wave being composed of short pulse components recurring atfrequencies at least as high as the line scanning frequency andrelatively long pulse components recurring at the field scanningfrequency, all said component pulses being of substantially rectangularshape and of constant amplitude, the combination of a thermionicdi'scharge device, means coupling said composite synchronizing Wave tothe input of said device, said means comprising a network for partiallyintegrating said Wave to increase the amplitude of portions of said waveduring the occurrence of said long pulses as compared with theamplitudes of other portions of said wave Without materially decreasingthe slopes of the edges of said pulses, means biasing said device toprevent ow of current in the output circuit thereof except during theoccurrence of said portions of increased amto provide synchronizingimpulses each of which has a sharply defined major peak. 11. In atelevision system wherein a eld deiiection generator is synchronizedfrom impulses derived from a composite synchronizing wave, said wavebeing composed of pulse components all of substantially equal amplitudeand rectangular wave form, said components including relatively shortpulses recurring at a high frequency equal to the line scanningfrequency or a multiple thereof and relatively long pulses recurring atthe eld scanning frequency, each of said long' pulses being interruptedsaid high frequencies, the combination comprising a thermionic dischargedevice having input and output circuits, means for coupling saidcomposite synchronizing wave to said input circuit,`

said means comprising an integrating network having a time constantsubstantially greater than the .duration of said short pulse componentsand less than the duration of said long components,

whereby said wave is partially integrated to distort said short pulsesinto peaked pulses and said long pulses into serrated pulses ofrelatively greater amplitude, means biasing said device to transmit tosaid output circuit only those portions of said serrated pulses whichexceed said peaked pulses in amplitude, and means for coupling saidoutput circuit to said deection generator-and for further modifying theWave shape of said transmitted portions to provide serrated fieldsynchronizing impulses each having an initial serration of greateramplitude than subsequent serrations, said last means comprising adifferentiating network.

ROBERT E. MOE.

for short intervals at one ofy.

